This invention relates to the field of electronic processing circuitry usable with analog data sources, such as light to electrical transducer elements, for amplifying, sampling, remembering, and converting analog input signals into digital output signals.
Present-day electronic hardware for military and commercial use is moving in the direction of decreased analog signal processing and increased digital signal processing, in either software or hardware form, for the analog signals obtained from a variety of signal sources. Generally, the signal source transducers coupled to these digital processors are responsive to varying phenomena according to some prearranged organizational pattern, such as scanning. An example of such signal sources is found in the video signal generating solid state arrays frequently used for scene scanning, large area signal reception, and other light communicated information. In military equipment, it is common practice to process a relatively large number of parallel occurring signals which originate with a terrain scene in order that a representation of the scene be, for example, stored in digital form or presented to a human operator as an array of pixels picture for decision-making purposes.
An additional example of the military use of such apparatus is found in the target drone aircraft used for experimental evaluations in the development of new anti-aircraft weapons systems. In this equipment the employed sensors usually include a plurality of solid state light-to-electrical transducers arranged in a large area physical array and located in reception areas of an unpiloted target aircraft; these sensors are subjected to radiation or varying degrees during a testing flight in order that radiation intensities, duration, frequency spectrum, and other characteristics be quantitatively measurable for use in establishing effectiveness criteria, determining atmospheric effects and measuring other performance factors. In this target aircraft sensor or in the scene scanning example a large number of possibly low level analog signals are received at the input of a data acquisition channel array for processing into digital signals.
Typically these systems further include in the order of 256 analog signals originating in the optical sensor array and having magnitudes as low as the nanoamp range that are to be processed under conditions of limited, battery-supplied processing energy and coupled to a common 8-bit data bus for transmission to a computer digital processing system. Moreover, the parallel nature of the 256 or more transducer input signals and the serial nature of computer-oriented processing, suggests a need for temporary signal storage at some point in the processing system. The present invention, therefore, includes capability for performing signal storage as well as amplification, and conversion of analog signals to digital signals.
The prior patent art includes several examples of signal processing arrangements of the general type described. Notable among these examples is the patent of Gyorgy I. Vancsa, U.S. Pat. No. 4,380,757, which relates to a data acquisition system having a plurality of parallel input channels communicated with a central processor by way of an analog-to-digital converter and a multiplexing communications bus arrangement. This communication arrangement is especially configured to lessen the calibration requirements on the large number of measurement channel circuits employed in the Vancsa apparatus. The Vancsa invention contemplates the use of sample signals, transformer AC coupling and a sample signal calibration method for operating the data channel apparatus.
The patent of Raymond B. Patterson, III, U.S. Pat. No. 4,282,515, discloses an analog-to-digital converter apparatus of the successive approximation type which employs a new encoder arrangement. The Patterson invention also includes sample and hold apparatus which operates in a multi-part cycle, allowing dual use of an incorporated amplifier circuit.
Another data collection system is shown in the patent of Richard A. Mazur et al, U.S. Pat. No. 4,125,831, which discloses a system for monitoring analog signals such as the output of a thermocouple temperature measuring probe. In the Mazur patent, the disclosed circuitry is energy supplied from a battery and is mounted in a moving container on a conveyer system. The Mazur apparatus also contemplates the temporary storage and transmission upon demand of the digital signals representing input data samples. The essence of the Mazur invention concerns the monitoring of temperature of a food can container as it passes through a complex path heating oven. This monitoring includes analog temperature sensing, data storage, and data retrieval upon demand at a predetermined conveyor location.
Another example of a prior art data acquisition apparatus is found in the patent of Jesse B. Lipcon, U.S. Pat. No. 3,982,241, which discloses an analog-to-digital conversion system wherein a single amplifier is shared between an analog-to-digital converter circuit and a sample and hold circuit in order that offset errors generated in one circuit cancel with the errors generated by the other circuit. The Lipcon apparatus includes amplifier circuitry, sample and hold circuitry, analog-to-digital converter circuitry, and the cancellation of spurious signals through a time-shared use of system components involved in spurious signal generation.
Another example of a data input channel apparatus is found in the patent of Andre Edourd Joseph Chatelon, U.S. Pat. No. 3,732,376, which concerns a time division multiplex apparatus employing a pair of sample and hold circuits and disclosing an arrangement for assigning certain of the input channels for use in the transmission of signalling and synchronizing data.
Although each of these prior art patents concerns a data input channel or portions thereof, none of these prior art arrangements is a suitable alternative for the improved capability data acquisition channel apparatus of the present invention.